1. Field of the Invention
This invention relates to high-power blue-violet III-nitride semipolar laser diodes (LDs).
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by one or more reference numbers within brackets, e.g., [Ref x]. A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
Conventional solid-state lighting systems use a III-nitride light-emitting diode (LED) that emits blue light to excite a phosphor, typically Ce-doped yttrium aluminium garnet (YAG), that emits yellow light. [Ref. 1] Some of the blue light from the LED is transmitted through the phosphor and is combined with the yellow light from the phosphor to create a dichromatic white light source. Although LEDs show promise for solid-state lighting applications, they nevertheless suffer from efficiency droop at high injection levels. [Ref. 2]
As an alternative to LEDs, LDs can be used to generate blue light. Since the carrier density in LDs clamps at threshold, there is no efficiency droop in LDs as in LEDs.
An advantage of using a LD instead of an LED is that the light emitted by a LD is spatially and temporally coherent, so both the directionality and efficiency of the light extraction can be precisely controlled through the design of the optical cavity. In contrast, the light emitted by an LED is spatially and temporally incoherent, meaning that some fraction of the light emitted by the LED is always going to be lost due to absorption at the backside of the LED, absorption at metal contacts on the top side of the LED, or potentially misdirected emission from the sidewalls of the LED.
Another advantage of LDs over LEDs is the current injection regime in which LDs operate. In order to achieve high EQEs, LEDs need to operate at low current densities. LDs, however, can achieve high EQEs at many orders of magnitude higher current density than LEDs. This will result in higher output power densities, which can be use to offset the cost of the substrates needed in the fabrication of the LDs.
Thus, there is a need in the art for improved methods of fabricating high-power blue-violet LD structures. The present invention satisfies this need.